Cahills are a type of Mayfly. They come in 2 flavors - light and dark. Fairly large, around size 14. Light Cahills have a tan/cream colored body with bronze/light dun wings.

They actually hatch around this time of year (although I haven't seen any yet) so this is a timely post. Light Cahills used to be prolific on the Deerfield but I think the greedy dam operators have blown most of the nymphs out by doing considerate things like blowing the dam at 3,000 cfs for days on end.